The present invention relates to rotary electric motors, more particularly to motor structure having electrical control and drive elements integrated therein.
The progressive improvement of electronic systems, such as microcontroller and microprocessor based applications for the control of motors, as well as the availability of improved portable power sources, has made the development of efficient electric motor drives for vehicles, as a viable alternative to combustion engines, a compelling challenge. Electronically controlled pulsed energization of windings of motors offers the prospect of more flexible management of motor characteristics. By control of pulse width, duty cycle, and switched application of a battery source to appropriate stator windings, functional versatility that is virtually indistinguishable from alternating current synchronous motor operation can be achieved. The use of permanent magnets in conjunction with such windings is advantageous in limiting current consumption.
The above-identified copending related U.S. patent application of Maslov et al., Ser. No. 09/826,422, identifies and addresses the need for an improved motor amenable to simplified manufacture and capable of efficient flexible operating characteristics. In a vehicle drive environment, it is highly desirable to attain smooth operation over a wide speed range, while maintaining a high torque output capability at minimum power consumption. Such a vehicle motor drive should advantageously provide accessibility to the various structural components for replacement of parts at a minimum of inconvenience. The copending related U.S. application incorporates electromagnet poles as isolated magnetically permeable structures configured in an annular ring, relatively thin in the radial direction, to provide advantageous effects. With this arrangement, flux can be concentrated, with virtually no loss or deleterious transformer interference effects in the electromagnet cores, as compared with prior art embodiments. While improvements in torque characteristics and efficiency are attainable with the structure of the identified copending application, further improvements remain desirable.
To this end, the above-identified copending related U.S. patent application of Maslov et al., Ser. No. 09/826,423, seeks to optimize rotor parameters such as the grade of the magnet, the energy density and the overall magnetic characteristics of the magnetic circuit, the size and the dimensions of which can adjust the permanence and the overall operating condition of the magnet when it is part of the rotor, the temperature stability of the magnet, magnet demagnetization, the finishing, coating and post processing steps taken in manufacturing of the magnets for the intended application, the stability of the magnetization over the curvilinear surface of the magnet, uniformity of the radial polarization of the magnet, the adjacent gap between two separate magnets, the mechanical features and geometry of the edges of the magnets, and the return flux path of the magnet as provided by a back iron ring section.
In environments in which portability and size are important factors, the need exists for drive motors that are capable of a wide range of operating characteristics, without sacrificing complex control functionality. Brushless motor systems must have the capability to control each of a plurality of electronic switches to provide accurate commutation sequencing and appropriate application of power to the individual stator windings. While the complexity of the electronic elements can be extensive and diverse, the need exists for a motor structural configuration in which the control elements that provide such operation are self-contained. Such a configuration should not be made at a sacrifice to cause limitations in the motor flux producing structure within a given constituent of the motor.
The present invention fulfills these needs, while taking advantage of the benefits of the isolated individual pole pair arrangements disclosed in the above identified Maslov et al. applications. The thin annular ring configuration of the stator is utilized to provide sufficient space in which to allocate a substantial portion, if not all, of a relatively complex electrical control system within the confines of the stator structure. Integration of the electrical control components within a shielded space internal to the stator flux producing structure provides several advantages. Simplification of integration and reduction of the number of individual discrete circuit elements are obtained while avoiding electromagnetic interference between the control circuit and the switched stator windings. When used, for example, in specific applications such as vehicle drives, the incorporation of both motor structure and the electrical control system within the vehicle wheel can provide a decrease in weight of the unit, while decreasing acoustic and mechanical noise. Operation from the user""s perspective can be simplified to simulate, for example, conventional automobile operation.
The aforementioned advantages are manifested in structural features of the invention, at least in part, wherein the motor comprises a rotor and stator each disposed in an angular ring configuration and spaced from each other by an annular air gap. The stator comprises a plurality of magnetically permeable core segments with coils wound thereon, the core segments being separated from direct contact with each other and disposed along the radial air gap. The segments thus are individual electromagnets. The inner radial periphery of the stator defines a space within which substantially no flux traverses. A controller is contained within the space for applying energization current to the stator windings. Also provided within this space are a power supply and electronic switches responsive to the controller for directing current pulses from the power supply individually to the stator windings. The power supply may comprise a plurality of replaceable batteries that are readily accessible to the user. The batteries may be capable of being recharged from an external source with or without their removal from the stator. Battery recharge may also be effected by regenerative current applied during operation by the stator segment windings. A rotor position sensor within the stator provides at least one output connected to the controller.
Preferably, each stator segment comprises a pair of poles circumferentially spaced from each other at the outer periphery and joined together by a yoke or linking portion at the inner periphery, the pair of poles having opposite magnetic polarities at the air gap when energization current is supplied to the segment winding. The winding of each stator segment may comprise two coil sections formed on a respective stator pole, each section being wound in opposite directions and connected in either series or parallel to provide, when energized, stator poles of opposite magnetic polarity. Alternatively, each stator segment may contain a winding formed entirely on the yoke or linking portion. Each stator segment winding is connected to a bridge configuration of the electronic switches. The direction of current flow in a winding for an energization pulse is established by the selected activation of the switches of the bridge in accordance with controller signals.
The controller may comprise circuitry distributed on a plurality of circuit boards upon which switches are also mounted. Alternatively, the controller may comprise an application specific integrated circuit (ASIC) in a single chip which may also integrate the switches. The width of the current pulses and the selection of the switches are controlled by the controller in response to signals received from one or more rotor position sensors that are mounted within the stator.
Additional advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description, wherein only the preferred embodiment of the invention is shown and described, simply by way of illustration of the best mode contemplated of carrying out the invention. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the invention. Accordingly, the drawings and description are to be regarded as illustrative in nature, and not as restrictive.